JAVA/heapSort.java
class Sort {
    public void heapSort(int arr[])
    {
        int temp;
 
        for (int i = arr.length / 2 - 1; i >= 0; i--)                //build the heap
        {
            heapify(arr, arr.length, i);
        }
 
        for (int i = arr.length - 1; i > 0; i--)                            //extract elements from the heap
        {
            temp = arr[0];                                                  //move current root to end (since it is the largest)
            arr[0] = arr[i];
            arr[i] = temp;
            heapify(arr, i, 0);                                             //recall heapify to rebuild heap for the remaining elements
        }
    }
 
    void heapify(int arr[], int n, int i)
    {
        int MAX = i; // Initialize largest as root
        int left = 2 * i + 1; //index of the left child of ith node = 2*i + 1
        int right = 2 * i + 2; //index of the right child of ith node  = 2*i + 2
        int temp;

        if (left < n && arr[left] > arr[MAX])            //check if the left child of the root is larger than the root
        {
            MAX = left;
        }
 
        if (right < n && arr[right] > arr[MAX])            //check if the right child of the root is larger than the root
        {
            MAX = right;
        }
 
        if (MAX != i) 
        {                                               //repeat the procedure for finding the largest element in the heap
            temp = arr[i];
            arr[i] = arr[MAX];
            arr[MAX] = temp;
            heapify(arr, n, MAX);
        }
    }
 
    void display(int arr[])                 //display the array
    {  
        for (int i=0; i<arr.length; ++i) 
        {
            System.out.print(arr[i]+" ");
        } 
    } 
 
    public static void main(String args[])
    {
        int arr[] = { 1, 12, 9 , 3, 10, 15 };
 
        Sort ob = new Sort();
        ob.heapSort(arr);
        ob.display(arr);
    }
}